Exemplary embodiments relate to a data output circuit and, more particularly, to a data output apparatus for controlling an output impedance.
A semiconductor device includes I/O pins for sending or receiving external data and a data output circuit for externally providing internal data. The I/O pins of a semiconductor device may be coupled to transmission lines, such as printed wirings on a substrate mounted on the semiconductor device. The internal data of a semiconductor device is provided to another semiconductor device through transmission lines (that is, through an interface). In order for the output data of a semiconductor device to be optimally transmitted through transmission lines, the output impedance of I/O pins is to be matched with the impedance of the transmission lines.
A data output circuit may include a pre-driver and a main driver. A main driver may control the output impedance of the I/O pins so that the output impedance is matched with the impedance of the transmission lines in order to support a high speed operation of the semiconductor memory device.
Meanwhile, a known data output circuit may supply the output signal of the pre-driver to the main driver regardless of a change in an output impedance of the main driver. Accordingly, a slew rate of an output signal varies according to the impedance of the main driver.